Name ___________________________ Class ___________________ Date _____________

Chapter 14 Work, Power, and Machines

Section 14.2 Work and Machines (pages 417–420)This section describes how machines change forces to make work easier to do.Input forces exerted on and output forces exerted by machines are identifiedand input work and output work are discussed.

Reading Strategy (page 417)

Summarizing As you read, complete the table for each machine. After you read, write a sentence summarizing the idea that yourtable illustrates. For more information on this Reading Strategy, seethe Reading and Study Skills in the Skills and Reference Handbookat the end of your textbook.

Machine Increases or Decreases Increases or DecreasesInput Force Input Distance

Tire jack

Lug wrench

Rowing oar

Summary: As input force decreases, the input distance increases.

Machines Do Work (pages 417–418)

1. Describe what a machine is able to do.

2. Is the following sentence true or false? A machine can make workeasier to do by changing the size of the force needed, the directionof a force, or the distance over which a force acts.

3. Consider the equation Work � Force � Distance. If a machineincreases the distance over which a force is exerted, the forcerequired to do a given amount of work .

4. Give an example of a machine that changes the direction of an applied force.

5. When you make several trips to unload a few heavy items from acar instead of moving them all at once, the total distance over whichyou exert yourself .

Work Input and Work Output (pages 419–420)

6. The work done by a machine is always less than the work done on amachine because of .

Physical Science Reading and Study Workbook ■ Chapter 14 163

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Decreases

Decreases

Increases

Increases

Increases

Decreases

A machine makes work easier to do by

changing a force.

true

decreases

Sample answers may include oars used in rowing.

increases

friction

7. Circle the letter of the definition for input force.a. the amount of force exerted by a machineb. the amount of friction slowing the speed of a machinec. the amount of work done by a machined. the amount of force exerted on a machine

8. Write a word equation that describes work input.

9. Is the following sentence true or false? Every machine uses someof its work input to overcome friction.

10. The force exerted by a machine is called the force.11. Circle the letter of the expression that equals the work output

of a machine.

a. b. Output distance � Input distance

c. d. Output distance � Output force

12. Is the following sentence true or false? Output work always is lessthan input work.

For questions 13 through 15, refer to the figure below.

13. Which arrow represents the input force? Label it on the figure.14. Which arrow represents the input distance? Label it on the figure.15. Which arrow represents the output force? Label it on the figure.16. How can you increase a machine’s work output?

Output distancefriction

Input distanceOutput distance

Name ___________________________ Class ___________________ Date _____________

Chapter 14 Work, Power, and Machines

164 Physical Science Reading and Study Workbook ■ Chapter 14

© Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reser ved.

Boat moves inthis direction.

Output distance

Work input equals the input force multiplied by the input distance.

true

output

true

The only way to increase work output

is to increase the amount of work put into a machine.